The Breakfast Study

• To compare the effects of breakfast meals containing low GI and high GI foods on glucose and insulin responses [ Time Frame: post ] [ Designated as safety issue: No ]
  

• To examine the effects of low and high GI meals on subjective ratings of hunger and subsequent food intake [ Time Frame: post ] [ Designated as safety issue: No ]
  
• To compare the effects of high protein meals containing either low or high GI foods with high carbohydrate meals containing either low or high HI food on glucose and insulin response, subjective ratings of hunger, and subsequent food intake. [ Time Frame: post ] [ Designated as safety issue: No ]
  

Each individual will participate separately in four testing sessions. Each testing session will last for approximately 5 hours and will be separated by a minimum of one week. Participants will arrive at the Temple University GCRC or CORE at either 7:30 a.m. or 8:30 a.m. after an overnight fast (10-12 hours) to ensure that all participants are in the same metabolic state. Upon arrival the experimenter will ask participants to complete a pre-session questionnaire and rate their feelings of hunger and satiety on a visual analog scale (VAS). An indwelling catheter will be inserted in an antecubital vein by the study nurse and a baseline blood sample will be obtained for measurement of glucose and insulin concentrations. Glucose will be measured by the glucose oxidase method using a glucose analyzer and insulin will be measured by radioimmunoassay.

One of four isocaloric meals (see example below), varying in macronutrient content and GI value of foods, will be administered in random order at either 8:00 a.m. or 9:00 a.m. Energy density will be controlled. The meal and 8 ounces of water will be consumed within fifteen minutes. A short visual analog questionnaire will be distributed at the conclusion of the meal to rate the meal consumed. Blood samples will be taken 15 minutes after food consumption and at 30 minute intervals (i.e., 30, 60, 90, 120, 150, 180, 210, and 240 minutes) over four hours following administration of the meal. Four milliliters of blood will be collected at each time point (via indwelling catheter), resulting in a total of 40 milliliters of blood collected at each study session and 160 milliliters (i.e., 40 ml x 4 testing sessions) within an 8 week time period. Participants will be asked to rate their feelings of hunger at these time points. Following the last blood sample, participants will be given the opportunity to consume food ad libitum from a buffet style lunch. Based on known serving sizes and measurements of unconsumed food, the amount of food eaten and its associated energy content will be determined.